Coloring substance-containing liquid crystal mixtures

Abstract

A liquid crystalline mixture comprising (a) at least one compound of the formula: <IMAGE> I wherein R1 is alkyl, alkoxy, p-alkylphenyl, p-alkoxyphenyl, trans-4-alkylcyclohexyl, 4'-alkyl-4-biphenylyl, p-(trans-4-alkylcyclohexyl)phenyl, 2-(trans-4-alkylcyclohexyl)ethyl or p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl and R2 is trans-4-alkylcyclohexyl; or R1 is trans-4-alkylcyclohexyl and R2 is p-(trans-4-alkylcyclohexyl)phenyl, p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl or 4'-(trans-4-alkylcyclohexyl)-4-biphenylyl; or R1 is p-alkylphenyl and R2 is p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl; and the alkyl and alkoxy groups in the substituents R1 and R2 are straight-chain groups of 1 to 7 carbon atoms, and; (b) at least one dichroic coloring substance selected from the group of compounds consisting of: <IMAGE> II <IMAGE> III <IMAGE> IV <IMAGE> IVa and <IMAGE> V wherein R3 is straight-chain C1-C12-alkyl and R4 is straight-chain C1-C4-alkyl, Z1 is hydrogen or chlorine, one of the symbols Z2, Z3 and Z4 is chlorine and the other two are hydrogen, and Y1 is hydrogen, Y2 is an amino group and Y3 is methyl or Y1 is hydroxy and Y2 and Y3 are hydrogen, and the use of these liquid crystalline mixtures in electro-optical devices are described.

We claim: 
     
       1. A liquid crystalline mixture comprising a. at least one compound of the formula: ##STR29## wherein R 1  is alkyl, alkoxy, p-alkylphenyl, p-alkoxyphenyl, trans-4-alkylcyclohexyl, 4'-alkyl-4-biphenylyl, p-(trans-4-alkylcyclohexyl)phenyl, 2-(trans-4-alkylcyclohexyl)ethyl or p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl and R 2  is trans-4-alkylcyclohexyl; or R 1  is trans-4-alkylcyclohexyl and R 2  is p-(trans-4-alkylcyclohexyl)phenyl, p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl or 4'-(trans-4-alkylcyclohexyl)-4-biphenylyl; or R 1  is p-alkylphenyl and R 2  is p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl; and the alkyl and alkoxy groups in the substituents R 1  and R 2  are straight-chain groups of 1 to 7 carbon atoms, and;   b. at least one dichroic colouring substance selected from the group of compounds consisting of: ##STR30## wherein R 3  is straight-chain C 1  -C 12  -alkyl and R 4  is straight-chain C 1  -C 4  -alkyl, Z 1  is hydrogen or chlorine, one of the symbols Z 2 , Z 3  and Z 4  is chlorine and the other two are hydrogen, and Y 1  is hydrogen, Y 2  is an amino group and Y 3  is methyl or Y 1  is hydroxy and Y 2  and Y 3  are hydrogen.   
     
     
       2. The liquid crystalline mixture of claim 1, wherein the colouring substance is about 0.2 to about 12 wt.% of the total weight of the mixture. 
     
     
       3. The liquid crystalline mixture of claim 1, wherein the compound of formula V is about 0.2 to about 6 wt.% of the total weight of the mixture. 
     
     
       4. The liquid crystalline mixture of claim 1, wherein the compound of formula IV is about 0.2 to about 4 wt.% of the total weight of the mixture. 
     
     
       5. The liquid crystalline mixture of claim 1, wherein the compound of formula IVa is about 0.2 to about 4 wt. % of the total weight of the mixture. 
     
     
       6. The liquid crystalline mixture of claim 1, wherein the compound of formula III is about 0.2 to about 4 wt.% of the total weight of the mixture. 
     
     
       7. The liquid crystalline mixture of claim 1, wherein the compound of formula II is about 0.2 to about 8 wt.% of the total weight of the mixture. 
     
     
       8. The liquid crystalline mixture of claim 1, wherein the coloring substance comprises: a. at least one compound of formula II;   b. at least one compound of formula III, IV or IVa; and   c. at least one compound of formula V.   
     
     
       9. The liquid crystalline mixture of claim 8, wherein the coloring substance is about 0.1 to about 0.4 part by weight of the compound of formula II per part by weight of the compound of formula V; and about 0.2 to about 0.6 part by weight of at least one compound of formulae III, IV or IVa per part by weight of the compound of formula V. 
     
     
       10. The liquid crystalline mixture of claim 1, wherein R 3  is a straight-chain C 5  -C 9  -alkyl, R 4  is methyl or ethyl, Z 4  is chlorine, and Z 2  and Z 3  are hydrogen. 
     
     
       11. The liquid crystalline mixture of claim 1, wherein the total amount of formula I compounds is about 7 to about 90 wt.% of the total weight of the mixture. 
     
     
       12. The liquid crystalline mixture of claim 1, wherein R 1  is alkyl, alkoxy, trans-4-alkylcyclohexyl, 4'-alkyl-4-biphenylyl or p-(trans-4-alkylcyclohexyl)phenyl and R 2  is trans-4-alkylcyclohexyl. 
     
     
       13. The liquid crystalline mixture of claim 1, wherein R 1  is trans-4-alkylcyclohexyl and R 2  is p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl or 4'-(trans-4-alkylcyclohexyl)-4-biphenylyl. 
     
     
       14. The liquid crystalline mixture of claim 1 further comprising at least one compound selected from the group of compounds consisting of: ##STR31## wherein R 7  and R 8  are straight-chain C 1  -C 7  -alkyl and ring A is 1,4-phenylene or trans-1,4-cyclohexylene; R 9  is straight-chain C 1  -C 12  -alkyl and R 10  is straight-chain C 1  -C 10  -alkyl, C 2  -C 10  -1-alkynyl, C 1  -C 10  -alkoxy, p-(C 1  -C 10  -alkyl)phenyl, p-(C 1  -C 10  -alkoxy)-phenyl or trans-4-(C 1  -C 10  -alkyl)cyclohexyl; R 11  and R 12  are straight-chain C 1  -C 12  -alkyl or if positioned on an aromatic ring R 11  and R 12  may also be straight-chain C 1  -C 12  -alkoxy, or one of R 11  and R 12  may also be a group of the formula: ##STR32## wherein X 1  and X 2  are independently single covalent bonds or one of X 1  and X 2  may also be --CH 2  CH 2  --; rings A 1  and A 2  are 1,4-phenylene or, when X 1  or X 2  is --CH 2  CH 2  --, rings A 1  and A 2  may also be trans-1,4-cyclohexylene; and R 13  is straight-chain C 1  -C 12  -alkyl or if positioned on an aromatic ring A 2 , R 13  may also be straight-chain C 1  -C 12  -alkoxy. 
     
     
       15. The liquid crystalline mixture of claim 1 further comprising at least one compound selected from the group of compounds consisting of: ##STR33## wherein R 7  is a straight-chain C 1  -C 7  -alkyl and ring A is 1,4-phenylene or trans-1,4-cyclohexylene. 
     
     
       16. The liquid crystalline mixture of claim 1 further comprising at least one compound of the formula: ##STR34## wherein X 8  is a single covalent bond or --COO--; X 7  is a single covalent bond, --COO--, --CH 2  CH 2  -- or, when X 8  is --COO--, X 7  may also be 1,4-phenylene; ring A 3  is a benzene ring or trans-1,4-cyclohexylene; ring A 4  is a benzene ring or, when X 8  is --COO-- and X 7  is a single covalent bond, --COO-- or --CH 2  CH 2  --, ring A 4  may also be trans-1,4-cyclohexylene; the symbols Z 5 , Z 6  and Z 7  are hydrogen or if positioned on a benzene ring which is not linked directly with a further ring via a single covalent bond Z 5 , Z 6  and Z 7  may also be halogen, cyano or methyl; Y 6  is cyano, nitro, 2,2-dicyanovinyl or, when Y 5  is hydrogen, Y 6  may also be 2,2-dicyano-1-methyl-vinyl; Y 5  is halogen, cyano, C 1  -C 3  -alkyl or, when X 7  is p-phenylene or Y 6  is nitro or at least one of Z 5  and Z 6  is other than hydrogen, Y 5  may also be hydrogen; and R 19  is C 1  -C 12  -alkyl or if positioned on a benzene ring, R 19  may also be C 1  -C 12  -alkoxy, or a compound of the formula: ##STR35## wherein R 21  is hydrogen, halogen or cyano; Y 4  is cyano, 2,2-dicyanovinyl or 2,2-dicyano-1-methylvinyl; R 20  and E together are p-R 20  -phenyl, trans-4-R 20  -cyclohexyl, R'-R 20  -4-biphenylyl, p-(trans-4-R 20  -cyclohexyl)phenyl, p-(5-R 20  -2-pyrimidinyl)phenyl, p-[2-(p'-R 20  -phenyl)ethyl]-phenyl, p-[2-(trans-4-R 20  -cyclohexyl)ethyl]-phenyl, trans-4-[2-(p-R 20  -phenyl)ethyl]-cyclohexyl or trans-4-[2-trans-4-R 20  -cyclohexyl)ethyl]cyclohexyl; and R 20  is straight-chain C 1  -C 12  -alkyl or if positioned on a benzene ring; R 20  may also be straight-chain C 1  -C 12  -alkoxy. 
     
     
       17. An electro-optical cell comprising: a. two plate means;   b. a liquid crystal means disposed between the two plate means comprising: (i) at least one compound of the formula: ##STR36## wherein R 1  is alkyl, alkoxy, p-alkylphenyl, p-alkoxyphenyl, trans-4-alkylcyclohexyl, 4'-alkyl-4-biphenylyl, p-(trans-4-alkylcyclohexyl)phenyl, 2-(trans-4-alkylcyclohexyl)ethyl or p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl and R 2  is trans-4-alkylcyclohexyl; or R 1  is trans-4-alkylcyclohexyl and R 2  is p-(trans-4-alkylcyclohexyl)phenyl, p-[2-trans-4-alkylcyclohexyl)ethyl]phenyl or 4'-(trans-4-alkylcyclohexyl)-4-biphenylyl; or R 1  is p-alkylphenyl and R 2  is p-[2-(trans-4-alkylcyclohexyl)ethyl]phenyl; and the alkyl and alkoxy groups in the substituents R 1  and R 2  are straight-chain groups of 1 to 7 carbon atoms, and;   (ii) at least one dichroic colouring substance selected from the group of compounds consisting of: ##STR37## wherein R 3  is straight-chain C 1  -C 12  -alkyl and R 4  is straight-chain C 1  -C 4  -alkyl, Z 1  is hydrogen or chlorine, one of the symbols Z 2 , Z 3  and Z 4  is chlorine and the other two are hydrogen, and Y 1  is hydrogen, Y 2  is an amino group and Y 3  is methyl or Y 1  is hydroxy and Y 2  and Y 3  are hydrogen; and     c. means for applying an electrical potential to said plate means.